1. Field of the Invention
The present invention relates to an Internet Protocol compliant private branch electronic exchange and a method for use thereon for expanding the number of terminal ports to fall under the control of the exchange and its program. In particular, the invention relates to the method for expanding the number of terminal ports to fall under the control of the exchange, by which the number of terminal ports to be accommodated and controlled by the Internet Protocol compliant private branch electronic exchange can be expanded.
2. Description of the Related Art
In a prior art Internet Protocol compliant private branch electronic exchange [hereinafter referred to as “IP-PBX” (Internet Protocol-Private Branch eXchange)], a Multimedia Gateway Controller (MGC) that performs call control/processing tasks has Local Area Network (LAN) ports and connects these ports to the Internet, an intranet, or LAN. In this case, the LAN is a network that may be Ethernet (registered trademark).
Using the MGC, the IP-PBX conducts control of Internet Protocol (IP) compliant phones (IP phones) that may connect to the Internet or an intranet and a terminal adapter (IPTA: Internet Protocol Terminal Adapter) which accommodates terminals not compliant with IP and attaches IP to the terminals. The most prior art IP-PBXs have the MGC built on a server processor and, therefore, accommodates LAN interfaces via Peripheral Component Interconnect (PCI) bridges or the like.
A configuration example of the above IP-PBX is shown in FIG. 16. Referring to FIG. 16, a method for use on the above IP-PBX for expanding the number of ports to fall under the control of the IP-PBX will be described. The prior art IP-PBX includes an MGC 61 and the MGC 61 has a main processor (MP) 62, a memory 63 connecting to the main processor 62, and a call control data master table 631 created in the memory 63.
The main processor 62 connects to a LAN interface 64-1 through a system bus 500 and the LAN interface 64-1 connects to a switching hub 5-1 via a LAN 200. The switching hub 5-1 connects to a router 6 and connects to a network [for example, a Wide Area Network (WAN) 300].
On the other hand, IP compliant phones (hereinafter referred to as “IP phones”) 7-1, 7-2 or an IP compliant terminal adapter (hereinafter referred to as “IPTA”) 8 that accommodates non-IP phones 9-1, 9-2 connects to a switching hub 5-2 and the switching hub 5-2 connects to the router 6 and connects to the network (for example, WAN 300).
The main processor 62 of the MGC 61 generates IP packets in a packet format of Transmission Control Protocol/Internet Protocol (TCP/IP) or User Datagram Protocol (UDP) and the LAN interface 64-1 transmits the IP packets.
On the other hand, IP packets from the terminals being under the control of the IP-PBX, such as the IP phone 7-1, are received by the LAN interface 64-1, and the main processor 62 extracts call control data from the IP packets. In this case, the main processor 62 has a function of layer 2 retransmission. Alternatively, the LAN interface 64-1 may have the functions of conversion to a packet format of TCP/IP or UDP and layer 2 retransmission. In this case, the main processor passes call control data to the LAN interface 64-1 without converting it into IP packets and the LAN interface 64-1 converts it into IP packets. Thereby, packets of IP packet format are sent and received between the LAN interface 64-1 and the terminals being under the control of the IP-PBX, such as the IP phone 7-1.
In the IP-PBX configuration as described above, when expanding the number of terminals falling under the control of the IP-PBX, namely, the IP phones 7-1, 7-2 and the IPTA 8 that are accommodated by the IP-PBX 60, is performed, the number of increasable terminals to fall under the control of the IP-PBX is determined by the upper limit of the IP packet handling capacity of the LAN interface 64-1 or the upper limit of the processing capacity of the main processor 62. To spare the LAN interface 64-1 reaching the upper limit of its IP packet handling capacity and share the load, the number of LAN interfaces 64-2, 64-3, etc. may be increased as much as the predefined number of the interfaces with the LAN 200.
When the number of terminals to fall under the control of the IP-PBX can no longer be increased even by increasing the number of the LAN interfaces; that is, when the main processor 62 has reached the upper limit of its processing capacity, the processor performance must be enhanced to provide more processing capacity. When a single MGC has reached the limit of expanding the number of terminals to fall under the control of the IP-PBX, a plurality of MGCs may be installed to share the load.
One problem associated with the above-described method for expanding the number of terminal ports to fall under the control of the IP-PBX, which has heretofore been used, is as follows. To expand the number of terminals such as IP phones and IPTAs to fall under the control of the IP-PBX, even if the number of LAN interfaces has increased for load sharing to relieve a LAN interface from exceeding its IP packet handling capacity, the processor used as the main processor must be altered for performance enhancement adaptive to more quantity of additional terminals because processing by software is required for a system in which the main processor performs the functions of generating IP packets and layer 2 retransmission, resulting in a high cost of the MGC.
Another problem is that, if retransmission on the network often occurs, it affects the call control itself and causes call control delay. If the same services and functions as provided by conventional PBXs not compliant with IP are realized on IP phones and IPTAs, the call control data to be communicated between the main processor and the terminals being under the control of the IP-PBX generally increases. Also, the prior-art IP-PBX presents a problem of increase in its cost when increasing the number of expandable terminal ports to fall under the control of the IP-PBX (with increase in the processing capacity of the main processor).
If the LAN interfaces have the functions of conversion to a packet format of TCP/IP or UDP and layer 2 retransmission, the main processor can be relieved from its overload state. However, if the terminals falling under the control of the IP-PBX are divided into some groups respectively using different protocols, the main processor still has the processing load in interpreting a plurality of different protocols. Under this condition, in order to expand the number of terminals to fall under the control of the IP-PBX, the main processor needs to increase its procession capacity (the processor must be altered for performance enhancement), resulting in the problem of a high cost of the MGC.
In order to process a plurality of different protocols, a proxy server for making protocol conversion may be installed within the LAN between the MGC and the terminals being under the control of the IP-PBX. A problem hereof is also the cost of the IP-PBX system that increases for the proxy server.
As described above, in the method for expanding the number of terminal ports to fall under the control of the IP-PBX in the prior art IP-PBX, there remain problems with scalability and flexibility for accommodating a plurality of different protocols.